Howto create certificate for server with multiple names

What is the best praticies to generate the csr certificate in this case? I am going to use CACert.
Should I use "common name" equal webmail.mydomain.br and "subjectAltNames" equal mailhost.mydomain.br or vice-versa?

If I use only one name in subjectAltNames my csr certificate there isn't SubjectAltName.
Look the command bellow.